1. Field of the Invention
The present invention generally relates to a technology for transmitting information on a change of shared data to a higher node computer while suppressing an overhead in a parallel computer system having a multi-stage multi-branch tree structure.
2. Description of the Related Art
Conventionally, there has been known a technique for transmitting and receiving data among a plurality of computers using internode communication by connecting the computers to one another, and for sharing the data among the computers. It is important particularly for a parallel computer system, in which a plurality of computers is connected to one another to act as if the node computers operate as one computer to keep consistency of the shared data.
However, it is difficult to keep the consistency of the shared data through the communication held in the parallel computer system because of frequent communications and heavy overhead of a processor using a context switch for the communications.
To solve the disadvantages, the following parallel computer system is disclosed in, for example, Japanese Patent Application Laid-Open No. H7-152640. The parallel computer system includes a shared-data managing unit. In the parallel computer system, a computer that changes shared data present in a common memory notifies the shared-data managing unit of a change in the shared data. The shared managing unit manages the change in the shared data based on the notification. According to the technique disclosed in the Japanese Patent Application Laid-Open No. H7-152640, it is possible to keep consistency of the shared data in the parallel computer system by causing computers other than the computer that changes the shared data to refer to the change in the shared data managed by the shared-data managing unit. Furthermore, overhead can be suppressed in the parallel computer system and the consistency of the shared data can be kept by using the above mechanism.
The conventional technique disclosed in the Japanese Patent Application Laid-Open No. H7-152640 has, however, the following disadvantages. Differently from an instance in which shared data is stored in the shared memory, if data dependency relationship is held among a plurality of computers in the parallel computer system, a higher node computer cannot determine whether data input from a lower node computer has had change.
Specifically, the parallel computer system has a multi-branch tree structure with one node configuration/topology. Due to this, information on the change in shared data made by the lower node computer can be promptly transmitted to all the other node computers. However, if the parallel computer system has a multi-branch tree structure with multiple-node configuration/topology and data held in each node computer depends on data held in the lower node computers, it is actually, disadvantageously difficult to transmit information on the change in the shared data up to the highest node computer because of the restrictions imposed by communication overhead.